[PATCH] D144838: [SCCP] Correct the made changes behavior

Tue Feb 28 03:04:54 PST 2023

bcl5980 added inline comments.

================
Comment at: llvm/lib/Transforms/IPO/SCCP.cpp:215

-        MadeChanges = true;
-
-        if (&BB != &F.front())
+        if (&BB != &F.front()) {
+          MadeChanges = true;
----------------
nikic wrote:
> Even in this case we're going to do a changeToUnreachable() below, so it's still changed?
Oh thanks for the mention. You are right, generally it will change first non-phi instruction to unreachable.
How about if the entry block is already unreachable? It will replace unreachable to unreachable again. It looks this case we needn't set MadeChanges to true.
I have some local code to run ipsccp until no changed and dead loop happen here. This is the motivation of the patch. And I think I need to find some other way to workaround it maybe.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144838/new/

https://reviews.llvm.org/D144838